Modular magnetic flux control

ABSTRACT

Modular coil assemblies for wireless charging of vehicles have coil geometries and communications designed to limit electromagnetic field (EMF) levels in regions where humans or other living objects may be present. The modular coil assemblies are designed with the ability to shape the magnetic field to be predominately within shielding provided by the auto chassis by, for example, providing side-by-side phase cancellation or diagonal versus front-to-back (for 1×3, 2×3 array configurations) phase cancellation. The power levels and frequency offset pairwise compensation of the respective coils may be controlled to improve cancellation and thus to reduce magnetic field exposure potential. The phase cancellation of the magnetic flux density from respective coil assemblies varies over a range to provide, for example, ˜50% cancellation at 125° offset and up to ˜100% cancellation at 180°. Charging profiles for vehicles and charging stations may be used to maximize the magnetic flux density cancellation during charging.

TECHNICAL FIELD

This patent application describes a wireless power transfer coil systemthat performs wireless charging through use of magnetic induction. Thewireless power transfer coil system includes a modular coil assemblythat allows for control of total magnetic flux produced.

BACKGROUND

Wireless Power Transfer (WPT) makes use of magnetic induction in an aircore transformer. Electrical power is sent from the sending apparatus tothe receiving apparatus by means of magnetic flux linkage between theprimary (transmitting) and secondary (receiving) coils as stated inFaraday's Law of magnetic induction.

Wireless power transmission via magnetic induction was introduced in the19th century but failed commercially due to a misunderstanding of theatmosphere's ability to form electrically conductive channels suitablefor long-range power transmission. An open-air transformer for wirelesspower transfer was patented by Nikola Tesla in an “Apparatus fortransmission of electrical energy,” U.S. Pat. No. 649,621, issued May15, 1900, and in a “System of transmission of electrical energy,” U.S.Pat. No. 645,576, issued Mar. 20, 1900.

In recent years, wireless power transmission via magnetic induction hasbeen used to charge electrical appliances and, more recently, to chargeelectric vehicles. Precise control of the magnetic flux is desirable forefficient power transfer and for minimization of magnetic flux leakageto the surrounding environment. For example, as described in U.S. Pat.No. 8,934,857, parasitic antennas have been used approximate thetransmit antenna to selectively modify a distribution of the generatedfield of a wireless power transmitter by, for example, expanding acoverage area of a small transmit antenna or concentrating a field of alarge transmit antenna.

SUMMARY

Various examples are now described to introduce a selection of conceptsin a simplified form that are further described below in the DetailedDescription. The Summary is not intended to be used to limit the scopeof the claimed subject matter.

In sample embodiments, a coil array is provided that includes an n×marray of coil assemblies, where n≥1 and m≥2, arranged in a rectilinearx-y grid pattern. Each coil assembly generates a charging signal at afrequency that is out-of-phase with a charging signal of a neighboringcoil assembly during a charging session whereby a charging signaltransmitted by a coil assembly destructively interferes with a chargingsignal transmitted by the neighboring coil assembly to reduce additivemagnetic flux density during charging as compared to additive magneticflux density where the neighboring coil assembly is in-phase duringcharging. The coil array may be mounted in the ground and furtherinclude a communication device associated with the coil array thatreceives setup parameters from a communication device associated with avehicle to be charged. A charging site server may provide chargingparameters of the coil array using the setup parameters. Application ofthe charging parameters to the coil array may cause generation ofadditive magnetic flux density during charging that remainspredominately within an exclusion zone for the vehicle.

Each coil assembly may be driven by a different power source and eachcoil assembly may transmit a charging signal having a determinedamplitude. The charging signal transmitted by the coil assembly may beapproximately 180° out of phase with the charging signal transmitted bythe neighboring coil assembly to provide the destructive interference.In sample embodiments, each coil assembly may generate a charging signalat the frequency where the charging signal is between 25° and 180°out-of-phase with a charging signal of an adjacent coil assembly duringa charging session while still yielding advantageous results.

In sample configurations of the coil array, where n=2 and m=2, the coilarray may comprise a first pair of coil assemblies disposed adjacenteach other and a second pair of coil assemblies disposed adjacent eachother and in parallel with the first pair of coil assemblies. The firstand second pairs of coil assemblies may be powered by respective firstand second power sources or each coil assembly may be powered by aseparate power source. Each of the first and second pairs of coilassemblies may share a same transmission frequency and power level butwith a set phase difference between the coil assemblies in each pair ofcoil assemblies to provide the desired destructive interference.

In other configurations of the coil array, where n=2 and m=2, the coilarray may comprise a first pair of coil assemblies disposed diagonallyfrom each other and a second pair of coil assemblies disposed diagonallyfrom each other and side-by-side in the x-y directions with the firstpair of coil assemblies. The first and second pairs of coil assembliesmay be powered by respective first and second power sources or each coilassembly may be powered by a separate power source. The first pair ofcoil assemblies may share a first frequency and power level and thesecond pair of coil assemblies may share a second frequency and powerlevel, the first and second frequencies being different, whereby eachcoil assembly has a set phase difference with adjacent coil assembliesin the x-y directions during charging.

In still other configurations of the coil array, where n=2 and m=2, thecoil array may comprise a first pair of coil assemblies disposedside-by-side with each other and a second pair of coil assembliesdisposed side-by-side with each other and in parallel with the firstpair of coil assemblies. The first and second pairs of coil assembliesmay be powered by respective first and second power sources or each coilassembly may be powered by a separate power source. The first pair ofcoil assemblies may share a first frequency and power level and thesecond pair of coil assemblies may share a second frequency and powerlevel, the first and second frequencies being different, whereby eachcoil assembly has a set phase difference with adjacent coil assembliesin the x-y directions during charging.

In further configurations of the coil array, where n=1 and m=3, the coilarray may comprise respective first, second and third coil assemblies ina row. The first and third coil assemblies may output first chargingsignals having a first frequency, phase, and power level. The secondcoil assembly may be disposed between the first and third coilassemblies and configured to output a second charging signal having thefirst frequency and power level but the second charging signal isout-of-phase with the first charging signal.

In yet further configurations of the coil array, where n=1 and m=3, thecoil array may comprise respective first, second and third coilassemblies in a row. The first and third coil assemblies may outputfirst charging signals having a first frequency, first phase, and firstpower level. The second coil assembly may be disposed between the firstand third coil assemblies and configured to output a second chargingsignal having the first frequency but the second charging signal isout-of-phase with the first charging signal and has a second power levelthat is different from the first power level that is set so as to reducethe additive magnetic flux density as compared to an additive magneticflux density where the first, second, and third coil assemblies outputcharging signals having a same power level. Advantageously, the firstand second power levels may be adjusted to shape the additive magneticflux density during charging to remain predominately within an exclusionzone for the vehicle.

In sample embodiments, the first and second power levels may be set so aregion where a maximum magnetic flux cancellation between the first andsecond charging signals occurs on a curve that is a function of acurrent ratio between the first and third coil assemblies versus thesecond coil assembly and a proportion of magnetic flux density canceledwhen the first and third coil assemblies carry current that isapproximately 180° out of phase with a current carried by the secondcoil assembly. The first and second power levels may be set toapproximate a point where a minimum magnetic flux cancellation betweenthe first and second charging signals is maximized.

In yet another configuration of the coil array, where n=2 and m=3, thecoil array may comprise a first pair of coil assemblies disposedadjacent each other, a second pair of coil assemblies disposed adjacenteach other, and a third pair of coil assemblies disposed adjacent eachother. Each pair of coil assemblies may be in parallel with each otherand output first charging signals having a first frequency. Each pair ofcoil assemblies may be powered by respective first and second powersources or each coil assembly in each pair may be powered by a separatepower source. A coil assembly of each pair of coil assemblies may outputa charging signal having a set phase difference with an adjacent coilassembly in the x-y directions during charging to provide the desireddestructive interference.

In a further configuration of the coil array, where n=2 and m=3, thecoil array may comprise a first pair of coil assemblies disposedadjacent each other, a second pair of coil assemblies disposed adjacenteach other, and a third pair of coil assemblies disposed adjacent eachother. Each pair of coil assemblies may be in parallel with each otherand output first charging signals having a first frequency. Each pair ofcoil assemblies may be powered by respective first and second powersources or each coil assembly in each pair may be powered by a separatepower source. A first coil assembly in each pair of coil assemblies mayhave a set phase difference with a second coil assembly of each pair ofcoil assemblies whereby a coil assembly of each pair of coil assembliesoutputs a charging signal having a same phase as a charging signaloutput by an adjacent coil assembly of an adjacent pair of coilassemblies.

In other sample embodiments, a wireless power transfer system isprovided that includes a vehicle coil array and a ground coil array. Thevehicle coil array may include an n×m array of vehicle coil assemblies,where n≥1 and m≥2, arranged in a rectilinear x-y grid pattern. Eachvehicle coil assembly may receive a charging signal at a frequency thatis out-of-phase with a charging signal of an adjacent vehicle coilassembly during a charging session whereby a charging signal received byeach vehicle coil assembly destructively interferes with a chargingsignal received by an adjacent vehicle coil assembly in the x-ydirections so as to reduce additive magnetic flux density duringcharging as compared to additive magnetic flux density where theadjacent vehicle coil assemblies in the x-y directions are in-phaseduring charging. Similarly, the ground coil array may comprise an r×sarray of coil assemblies, where r≥n and s≥m, arranged in a rectilinearx-y grid pattern. Each ground coil assembly may generate the chargingsignal at the frequency whereby the charging signal is out-of-phase withthe charging signal of an adjacent ground coil assembly during acharging session and whereby the charging signal generated by eachground coil assembly destructively interferes with the charging signalgenerated by an adjacent ground coil assembly in the x-y directions soas to reduce additive magnetic flux density during charging as comparedto additive magnetic flux density where the adjacent ground coilassemblies in the x-y directions are in-phase during charging.

In sample embodiments of the wireless power transfer system, the groundcoil array may detect when a vehicle coil assembly is inoperative andactivate only the ground coil assemblies aligning with operative vehiclecoil assemblies to send charging signals. A data repository may also beprovided that is accessible by the vehicle coil array and/or the groundcoil array during a charging session to access a charging profile ofdefault and historical measurements for each vehicle coil assembly. Thecharging profile may include frequency response and charging models forsetting charging parameters during the charging session.

In the sample embodiments of the wireless power transfer system, thecharging profile may include vehicle coil assembly frequency offset;make, model, and manufacturer of the ground coil assembly; a number ofvehicle coil assemblies; positioning of the vehicle coil assemblies;minimum and maximum current and voltage support of the vehicle coilassembly; health status of the vehicle coil assemblies; temperaturelimitations of the vehicle coil assemblies; temperature readings ofvehicle coil assemblies; and/or cooling availability for the vehiclecoil assemblies. The ground coil array also may obtain a number andplacement of vehicle coil assemblies of a vehicle to be charged from thecharging profile for the vehicle to be charged and select, for sendingcharging signals, a pattern of ground coil assemblies from the r×s arrayof coil assemblies corresponding to the number and placement of thevehicle coil assemblies for the vehicle to be charged.

In other sample embodiments of the wireless power transfer system, thedata repository may further store charging parameters for the groundcoil assembly including magnetic signal characteristics for each groundcoil assembly or pair of ground coil assemblies based on an alignedvehicle coil assembly or pair of vehicle coil assemblies. The chargingparameters for the ground coil assembly may include instantaneous powerlevel during a charging session, charging signal frequency, frequencydrift, signal phase offset, and/or nominal coil-to-coil gap. Thecharging parameters for the ground coil assembly also may include poweravailability; environmental factors; and/or ground coil assemblyconditions including internal temperature, usage, number of coils perground coil assembly, number of turns per ground coil assembly, and/orwhether the ground coil assembly is surface mounted or flush mounted.The charging parameters for the ground coil assembly may further includemake, model, and manufacturer of the ground coil assembly; autonomousalignment capability of the ground coil assembly; minimum and maximumcurrent and voltage support of the ground coil assembly; communicationsprotocols available to the ground coil assembly; and/or a communicationsbandwidth of the ground coil assembly.

In further sample embodiments, a wireless power transfer system isprovided that includes a vehicle coil array and a ground coil arraywhere the vehicle coil array transmits energy to the ground coil array.The vehicle coil array includes an n×m array of vehicle coil assemblies,where n≥1 and m≥2, arranged in a rectilinear x-y grid pattern. Eachvehicle coil assembly may generate a charging signal at a frequencywhereby the charging signal is out-of-phase with a charging signal of anadjacent vehicle coil assembly during a charging session and whereby acharging signal generated by each vehicle coil assembly destructivelyinterferes with the charging signal generated by an adjacent vehiclecoil assembly in the x-y directions so as to reduce additive magneticflux density during charging as compared to additive magnetic fluxdensity where the adjacent vehicle coil assemblies in the x-y directionsare in-phase during charging. The ground coil array may include an r×sarray of ground coil assemblies, where r≥n and s≥m, arranged in acongruent rectilinear x-y grid pattern. Each ground coil assembly mayreceive the charging signal at the frequency whereby the charging signalis out-of-phase with the charging signal of an adjacent ground coilassembly during a charging session and whereby the charging signalreceived by each ground coil assembly destructively interferes with thecharging signal received by an adjacent ground coil assembly in the x-ydirections so as to reduce additive magnetic flux density duringcharging as compared to additive magnetic flux density where theadjacent ground coil assemblies in the x-y directions are in-phaseduring charging.

In another sample embodiment of a wireless power transfer system, thevehicle coil array is larger than the ground coil array. This embodimentincludes a ground coil array comprising an n×m array of ground coilassemblies, where n≥1 and m≥2, arranged in a rectilinear x-y gridpattern. Each ground coil assembly may generate a charging signal at afrequency whereby the charging signal is out-of-phase with a chargingsignal of an adjacent ground coil assembly during a charging session andwhereby a charging signal generated by each ground coil assemblydestructively interferes with the charging signal generated by anadjacent ground coil assembly in the x-y directions so as to reduceadditive magnetic flux density during charging as compared to additivemagnetic flux density where the adjacent ground coil assemblies in thex-y directions are in-phase during charging. The vehicle coil array maycomprise an r×s array of vehicle coil assemblies, where r≥n and s≥m,arranged in a rectilinear x-y grid pattern. Each vehicle coil assemblymay receive the charging signal at the frequency whereby the chargingsignal is out-of-phase with the charging signal of an adjacent vehiclecoil assembly during a charging session and whereby the charging signalreceived by each vehicle coil assembly destructively interferes with thecharging signal received by an adjacent vehicle coil assembly in the x-ydirections so as to reduce additive magnetic flux density duringcharging as compared to additive magnetic flux density where theadjacent vehicle coil assemblies in the x-y directions are in-phaseduring charging.

An electric vehicle charging system is also provided that includes aplurality of coil arrays where each coil array comprises at least onecoil assembly that generates a charging signal at a set frequency. Atleast one sensor is also provided to measure aggregate magnetic fluxgenerated by charging signals generated by the coil arrays. Means arealso provided for identifying an additive hot spot of magnetic fluxdensities and for adjusting power, phase, and/or frequency offsets of atleast one of the coil arrays in a vicinity of the additive hot spot ofmagnetic flux densities to reduce magnetic flux densities at theadditive hot spot of magnetic flux densities.

Methods of charging an electric vehicle are also described whereby acharging point and the electric vehicle initiate communications witheach other and the charging point receives setup data from the electricvehicle for setting up the charging point for charging of the electricvehicle. The setup data may include a manufacturer of the electricvehicle, a model of the electric vehicle, and/or an exclusion zone. Thecharging point then activates the ground primary coils and associatedpower levels for the activated ground primary coils based on the setupdata to create a charging signal having a magnetic flux density thatdoes not extend beyond the exclusion zone. For example, the manufactureror model of the electric vehicle may be used to look up in a databasewhich ground primary coils to activate and power levels for theactivated ground primary coils. The charging point may activate theground primary coils according to a determined layout of the secondarycoils of the electric vehicle as determined from the received setupdata. The charging point may further adjust parameters of the chargingsignal based on the setup data as needed to fit a magnetic fluxgenerated by the charging signal within the exclusion zone.

In sample embodiments, the charging point and the electric vehicle mayinitiate communications with each other by the charging point emittingan inductive communications beacon while in a standby state andreceiving a response from the electric vehicle to establish that theelectric vehicle is approaching the charging point.

This summary section is provided to introduce aspects of the inventivesubject matter in a simplified form, with further explanation of theinventive subject matter following in the text of the detaileddescription. The particular combination and order of elements listed inthis summary section is not intended to provide limitation to theelements of the claimed subject matter. Rather, it will be understoodthat this section provides summarized examples of some of theembodiments described in the Detailed Description below.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other beneficial features and advantages of theinvention will become apparent from the following detailed descriptionin connection with the attached figures, of which:

FIG. 1 illustrates the high-level component design of a conventionalsecondary coil assembly and primary coil assembly.

FIG. 2 illustrates the additive destructive cancellation of twosinusoidal signals.

FIG. 3A geometrically illustrates the physical characteristics of anin-line pair of primary coil assemblies in a sample embodiment.

FIG. 3B geometrically illustrates the physical characteristics of asingle parallel pair of primary coil assemblies in a sample embodiment.

FIG. 3C geometrically illustrates the physical characteristics ofparallel pairs of primary coil assemblies in a sample embodiment.

FIG. 4 topographically illustrates the magnetic flux density created bya single primary and secondary coil assembly duo during a chargingsession.

FIG. 5A topographically illustrates the magnetic flux density created bya pair of modular in-line primary and secondary coil assembly duosduring an in-phase charging session.

FIG. 5B topographically illustrates the magnetic flux density created bya pair of modular in-line primary and secondary coil assembly duosduring an out-of-phase charging session.

FIG. 5C topographically illustrates the magnetic flux density created bya pair of modular parallel primary and secondary coil assembly duosduring an out-of-phase charging session.

FIG. 6A illustrates the magnetic flux density created by a 2×2 clusterof four modular primary and secondary coil assembly duos during anin-phase charging session.

FIG. 6B illustrates the magnetic flux density created by a 2×2 clusterof four modular primary and secondary coil assembly duos pairedside-by-side during an out-of-phase charging session. In thisconfiguration, diagonal duos are in-phase and adjacent duos areout-of-phase.

FIG. 6C illustrates the magnetic flux density created by a 2×2 clusterof four modular primary and secondary coil assembly duos paireddiagonally during an out-of-phase charging session with each pairoperating at a distinct frequency.

FIG. 6D illustrates the magnetic flux density created by a 2×2 clusterof four modular primary and secondary coil assembly duos pairedside-by-side during an out-of-phase charging session. In thisconfiguration, diagonal duos are out-of-phase.

FIG. 7A illustrates the magnetic flux density created by a 1×3 inlinecluster of three modular primary and secondary coil assembly duos duringan in-phase charging session.

FIG. 7B illustrates the magnetic flux density created by a 1×3 inlinecluster of three modular primary and secondary coil assembly duos duringan out-of-phase charging session.

FIG. 7C illustrates the magnetic flux density created by a 1×3 inlinecluster of three modular primary and secondary coil assembly duos duringan out-of-phase charging session with power control.

FIG. 7D illustrates the range of flux cancellation achievable in a 1×3inline cluster of three modular primary and secondary coil assembly duosduring an out-of-phase charging session with power control.

FIG. 8A illustrates the magnetic flux density created by a 2×3 clusterof six modular primary and secondary coil assembly duos during anin-phase charging session.

FIG. 8B illustrates the magnetic flux density created by a 2×3 clusterof six modular primary and secondary coil assembly duos during a duringa diagonal pairwise out-of-phase charging session.

FIG. 8C illustrates the magnetic flux density created by a 2×3 clusterof six modular primary and secondary coil assembly duos during aside-by-side pairwise out-of-phase charging session.

FIG. 9 illustrates exemplary placement of a single secondary coilassembly installation for a sedan type electric vehicle.

FIG. 10 illustrates exemplary placement of a single pair of secondarycoil assembly installations for a van type electric vehicle.

FIG. 11 illustrates exemplary placement of a cluster of three secondarycoil assembly installations for a transit bus type electric vehicle.

FIG. 12 illustrates exemplary placement of a cluster of six secondarycoil assembly installations for commuter bus type electric vehicle.

FIG. 13 illustrates a plot of the cancellation of magnetic flux versusdiagonal pairwise phase differences for a 2×2 cluster of four primaryand secondary coil assembly duos.

FIG. 14 illustrates the high-level component design for a wireless powertransfer system in a sample embodiment.

FIG. 15 diagrammatically illustrates the subsystems of an electricvehicle involved in a wireless charging session.

FIG. 16 illustrates the over-the-air signaling for an inductivelycoupled wireless charging session.

FIG. 17 shows a method of charging an electric vehicle in a sampleembodiment.

FIG. 18 graphically illustrates a charging station equipped with widearea magnetic flux management in a sample embodiment.

DETAILED DESCRIPTION

Embodiments of the wireless power transfer coil system and associatedmethod described herein may be understood more readily by reference tothe following detailed description taken in connection with theaccompanying figures and examples that form a part of this disclosure.It is to be understood that this description is not limited to thespecific products, methods, conditions, or parameters described and/orshown herein, and that the terminology used herein is for the purpose ofdescribing particular embodiments by way of example only and is notintended to be limiting of any claimed subject matter. Similarly, anydescription as to a possible mechanism or mode of action or reason forimprovement is meant to be illustrative only, and the subject matterdescribed herein is not to be constrained by the correctness orincorrectness of any such suggested mechanism or mode of action orreason for improvement. Throughout this text, it is recognized that thedescriptions refer both to methods and systems/software for implementingsuch methods.

A detailed description of illustrative embodiments will now be describedwith reference to FIGS. 1-18. Although this description provides adetailed description of possible implementations, it should be notedthat these details are intended to be exemplary and in no way delimitthe scope of the inventive subject matter. Note that the term “battery”is used herein to depict a generic chemical energy storage system andcould be replaced, supplemented, or hybridized with other portableenergy storage systems (e.g., solid-state batteries, reversable fuelcells, ultra-capacitors). Also, while many of the examples used are of awireless power transfer (WPT) system used to power the onboard systemsand charge the batteries of a stationary electric vehicle (EV), this useis by no means the only use contemplated.

The ability to transfer power over a magnetic link between a pairedconductive primary and secondary conductive coils is well-known. Suchsystems are commonly known as Wireless Power Transfer (WPT) systems. Amodular WPT based on symmetric coils deployed in clusters has been foundto provide advantages in manufacturability, deployment flexibility,dynamic provisioning, and high-power transfer efficiency.

Magnetic flux produced by the coil pair of an open-core transformerbased wireless power transfer system scales with transmitted powerlevel. In high power systems, magnetic flux can create electromagneticnoise and exceed human exposure limits. As high-power charging is neededby the electric vehicle market to minimize charging times, techniquesfor managing the magnetic flux are desired.

All air core transformer-based WPT systems produce magnetic flux thatextends beyond the immediate vicinity of the WPT system. Most (>95%) ofthe energy associated with this flux is recirculated into thecapacitance of the WPT transformer circuit each alternating currentcycle. Most (>99%) of the energy that is not recirculated becomesthermal energy in magnetic, dielectric, and conductive materials in andaround the coils. A small percentage of the energy is radiated and theradiofrequency (RF) electromagnetic waves associated with this energyare a form of non-ionizing radiation (NIR). The energy transferindicates that the vast majority of magnetic flux passes between themagnetic coils and that this area (Zone 1) exceeds human and electronicsexposure limits. The near-field magnetic flux density outside the coilperimeters but inside the periphery of the electric vehicle (i.e., inthe Exclusion Zone or Zone 2) may exceed human and/or electronicsexposure limits. Outside the Exclusion Zone delineation (Zone 3), thetotal magnetic flux density realized decreases monotonically outside theset threshold.

The measurable magnetic flux occurs predominately within Zones 1 and 2,that is within the exclusion zone delineation. Outside the exclusionzone, only magnetic flux density below a threshold is allowable. Theexclusion zone threshold may be set through legal or regulatory bodies,by the decision of the operator, or by the limits of human perception ofmagnetic effects.

For electromagnetically short antennas, such as the primary coil of aWPT system, the near field (reactive) range is defined as distance fromthe antenna 0 to λ/2π, where λ is wavelength. With an exemplary 85 kHzWPT system, this means that the near field range is over 561 meters inrange and the magnetic field strength and magnetic field power drop atrates of 1/(r³) and 1/(r⁶), respectively, (where r=radius) for themagnetic charging signal in the near field. The magnetic field strength(H-field, measured in amps per meter) is equal to the magnetic fluxdensity (B-field, measured in teslas) times a proportionality constantin the linear magnetic materials and in nonmagnetic materials (like air,fiberglass, vacuum etc.)

The recirculating flux that stores the inductive energy of the systemand mediates the power transfer is not radiation but may be present inareas where humans can be exposed to it. Guidelines for human exposureto these RF electromagnetic fields (EMFs) may be found in the Instituteof Electrical and Electronics Engineers document C95.1-2019-IEEEStandard for Safety Levels with Respect to Human Exposure to Electric,Magnetic, and Electromagnetic Fields, 0 Hz-to-300 GHz and in theInternational Commission on Non-Ionizing Radiation Protection (ICNIRP)document entitled GUIDELINES FOR LIMITING EXPOSURE TOELECTROMAGNETICFIELDS (100 KHZ-TO-300 GHZ).

It is in both the manufacturer's and user's interests to reduce RF EMFsproduced by WPT systems to allow for higher system power throughputwhile ensuring compliance with exposure guidelines. Since lowercoil-to-coil efficiency is associated with correspondingly increasedlevels of un-recirculated magnetic flux, it is in the manufacturer's anduser's interests to minimize un-recirculated magnetic flux regardless ofexposure guidelines.

Both active and passive magnetic field reduction methods are well knownin the art. Active systems, such as the Helmholtz coil and Maxwell coil,are well-known examples where auxiliary coils are used to createconstant field volumes where external magnetic fields can be suppressed.

Passive magnetic shielding uses ferromagnetic materials with highrelative permeability and a high saturation point to channel magneticflux or diamagnetic materials to shift flux. Examples of these materialsmay be found in ASTM A753-08 (2013); “Standard Specification for WroughtNickel-Iron Soft Magnetic Alloys” and MIL-N-14411 Revision C, Nov. 23,1977; “NICKEL-IRON ALLOY, HIGH MAGNETIC PERMEABILITY, SHEET, STRIP, ANDWIRE”.

However, both the active and passive approaches have been found to havedeficiencies for use in a wireless power transfer system beyond theefficacy to suppress undesired magnetic flux. For example, the activeapproach may require installation of additional magnetic structures(e.g. windings, radiators, loop(s)) which then need to be powered togenerate the cancellation signal of the correct amplitude, frequency,and phase. One example of this active, parasitic approach can be foundin U.S. Pat. No. 9,306,635. In many active cases, one or moremagnetically sensitive antennas will be necessary to create a feedbackcontrol loop. The active control system, due to the powered parasiticcancellation loops, will necessarily lower power transfer efficiency ofthe WPT system. On the other hand, the passive system suffers from boththe initial cost of materials, installation and deployment and theongoing cost for the maintenance of the contrivance needed tomechanically maneuver the shielding into place prior to and after eachwireless charging session.

A coordinated magnetic flux reduction system and method in a sampleembodiment does not require parasitic loops nor movement of shieldingmaterial, raising the power efficiency, and removing the need for movingparts. The coordinated magnetic flux reduction system described hereindoes not require fielding of additional equipment beyond the wirelesspower transfer apparatus. As will be understood by those skilled in theart, a coordinated magnetic flux reduction system may require a modularprimary coil construction with two or more co-deployed primary coilassemblies serving matching secondary coil assemblies.

In the coordinated cancellation approach, deploying power-transferringprimary and secondary coils (duos) in clusters with pairing betweenneighboring duos and adjusting the charging signal voltage, current andphase results in the summed magnetic flux produced by the WPT system tobe vastly reduced. There is no need for ancillary, non-power transfercancellation loops or coils. Supported cluster configurations of coilsinclude, for example, 1-by-2, 2-by-2, 2-by-3 and so on. Unpaired clusterconfigurations (e.g., 1-by-3, 1-by-5) can also benefit from virtualpairing of neighboring and/or adjacent coils in a cluster where thevoltage, current and phase is adjusted for each coil in the cluster.

Clusters may be sized for a particular use (e.g., electric vehicleclass—car, light truck, etc.) to allow for dynamic selection primarycoils based on matching the size and geometry of the secondary coilcluster. Depending on the ground deployment, the clustering can bedynamically provisioned. In one example, an Electric Vehicle (EV) with a2-by-1 secondary cluster can be charged by a 3-by-2 ground cluster andtake advantage of the phase, voltage, and current controlled powertransfer for each the aligned coil pairs to reduce magnetic flux.

Utilizing 2-way communications between the charger and equipment ordevice to be charged (e.g. as in U.S. Pat. No. 10,135,496, entitled“Near field, full duplex data link for use in static and dynamicresonant induction wireless charging”) not only allows forcommunications of near real-time events and status (e.g. battery chargelevel), but also allows exchange of information between the vehiclecontroller (e.g., a battery management system (BMS)) and the chargingstation (e.g., the charging station controller that tasks each GA andeach GA cluster) about the capabilities for each system.

The contours of constant magnetic flux density shown in FIGS. 4 through8C herein are dependent on the power transferred between the primary andsecondary coil assemblies. For each figure, the global flux densityscales linearly with the primary coil current so that changes to theinput current to the cluster of primary coil assemblies would contractor expand the contour lines spacing but not change overall the shape ofthe topographical mapping of contours of flux density. This holds truefor each cluster and for each current-phase relationship shown.

FIG. 1

FIG. 1 illustrates in exploded view the major components of aconventional primary and secondary coil assembly duo 100 for theinductively coupled wireless transfer of power.

In an exemplary embodiment, the secondary coil assembly 105 is installedunder an electric vehicle (EV) with necessary connections to thevehicle's battery management system (BMS) (not shown). In thisembodiment, the secondary coil assembly 105 is attached to the undersideof the EV, although other mounting positions are possible.

The EMF shield 101 serves to provide mechanical and electrical powerinterconnection to the EV while also preventing eddy currents from beinginduced on the EV's metal components.

The secondary backing core 102, nominally a continuous flat slab orshaped continuous sheet of ferrite material, serves to redirect magneticflux away from the vehicle. The terms “backing core” and “ferrite” asused to describe materials used to guide magnetic flux and are not meantto limit the selection of such materials. Both terms are used herein asa generic for any a construction of high-permeability magnetic material,with high-permeability meaning a relative permeability substantiallylarger than 1 (nominally >100). The term ferrite is not meant topreclude this use of other similar or compatible materials that could beused in construction of a backing core and may include layered metallicsheets, powdered oxides, sintered powdered oxides, and/or amorphousmetals that can be fabricated into the flat slab or shaped sheettopologies.

The secondary coil 103 is the receiver for the magnetically transferredenergy and may comprise a planar spiral of conductors (i.e., windings).The spiral can be either circular or rectangular and is smaller in areaor diameter than the backing core 102 and the EMF shield 101. A samplespiral coil configuration is described with respect to FIGS. 7-10 ofU.S. patent application Ser. No. 16/615,290, entitled “WIRELESS POWERTRANSFER THIN PROFILE COIL ASSEMBLY,” the contents of which areincorporated herein by reference.

The secondary coil assembly cover 104 is a lightweight, magneticallyinert housing to protect the electronics from liquid and dustincursions.

In the embodiment of FIG. 1, the primary coil assembly 110 is installedon the surface of pavement or underground to be flush with thepavement's surface.

The primary coil assembly cover 106 is a magnetically inert housingcapable of handling heavy loads while preventing liquid and dustincursions into the primary coil assembly 110.

The primary coil 107 is the transmitter for the magnetically transferredenergy and may comprise a planar spiral of conductors (i.e., windings).The spiral can be either circular or rectangular. In the interest ofminimizing unwanted magnetic flux production, the primary coil 107 andsecondary coil 103 are identical in area or diameter but may containcoil windings with a differing number of turns. It is noted that in abi-directional system the primary coil 107 and the secondary coil 103can swap duties and directions allowing power to be transmitted from thevehicle to the ground.

The primary backing core 108, nominally a continuous flat slab or shapedcontinuous sheet of ferrite material, serves to redirect magnetic fluxaway from the ground and back toward the secondary coil 103.

The ground plate 109 serves to mechanically support the rest of theprimary coil assembly. The ground plate may also provide interconnectionto electrical ground. Omitted from FIG. 1 are the electrical connectors,structural members, cooling plumbing, and sensors that do not materiallyaffect the magnetic field characteristics.

FIG. 2

FIG. 2 illustrates an example of the destructive cancellation of pairedsinusoids. The first signal 201, plotted by time (X-axis) and amplitude(Y-axis), shows the properties of wavelength 202, amplitude 203, and aphase of zero (0). A second signal 205 is also shown, plotted by time(X-axis) and amplitude (Y-axis). The second signal 205 has an amplitude206 and a wavelength 207 identical to the first signal 201; however, thephase difference 208 is 180°. When signal 201 and 205 are summed, theresultant signal 209 as shown plotted on a 3rd time (X-axis) andamplitude (Y-axis) coordinate system is nulled by destructiveinterference due to the 180° phase difference between signals 201 and205.

FIG. 3A

FIG. 3A illustrates the physical characteristics of a paired set 300 ofin-line modular primary coil assemblies (also known as a Ground Assembly(GA)). The primary coils can be rectangular (typically square) orelliptical (typically) circular) spirals. The first primary coilassembly 301 is emplaced with the adjacent and adjoining second primarycoil assembly 302. The adjacent primary coil assemblies 301 and 302 areseparated by a gap 304. In this example, the adjacent primary coilassemblies 301 and 302 are identical in length 305 and width 306 and arealigned in-line with the direction of movement 310 of the vehicle to becharged along an axis 303 and rectilinear in relation. The midpoints 307and 308 (a.k.a. the boresights) of the adjacent primary coil assemblies301 and 302 are separated by a distance 309.

The gap 304 serves to isolate the individual modular primary coilassemblies 301 and 302 both electrically and magnetically. Since thebacking core layer and EMF shield are larger than the coil windings (asshown in FIGS. 7-10 of U.S. patent application Ser. No. 16/615,290,“WIRELESS POWER TRANSFER THIN PROFILE COIL ASSEMBLY”), the gap 304 is adistance between EM shields of neighboring coil assemblies. Magneticisolation is achieved by sizing the gap 304 to prevent addition (orsubtraction by destructive cancellation) of magnetic flux from a firstprimary coil assembly 301 to the second primary coil assembly 302 aswell as from a primary to non-aligned nearby secondary coil assemblies.To create larger clusters based on the in-line configuration, additionalsecondary assemblies (and corresponding ground-based primary assemblies)may be added to the end of the cluster up to the length of the vehiclechassis, maintaining the requisite separation gap 304 between adjoiningsecondary assemblies. The front of the in-line cluster is defined as tothe left 310 in FIG. 3A in the direction of movement of the vehicle tobe charged.

FIG. 3B

FIG. 3B geometrically illustrates the physical characteristics of acharge point cluster 311 having a single parallel pair of primary coilassemblies in a sample embodiment. The primary assembly coils can berectangular (typically square) or elliptical (typical circular) spirals.The first primary coil assembly 301 is emplaced with the adjacent andadjoining second primary coil assembly 302 with both assemblies 301 and302 symmetrically placed to either side of the vehicle chassis midline303. The adjacent primary coil assemblies 301 and 302 are separated by agap 304. In this example, the adjacent primary coil assemblies 301 and302 are identical in length 305 and width 306 and are aligned along theaxis 303 and rectilinear in relation. The midpoints 307 and 308 (a.k.a.the boresights) of the adjacent primary coil assemblies 301 and 302 areseparated by a distance 309. The front of the parallel 311 cluster isdefined as to the left 310 in FIG. 3B in the direction of movement ofthe vehicle to be charged.

FIG. 3C

FIG. 3C geometrically illustrates the physical characteristics of a 2×2cluster 312 of primary coil assemblies with the first pair 301, 302 andsecond pair 313, 314 arranged in parallel rows with one member of eachpair situated to either side of the vehicle chassis centerline 303. Thefirst parallel primary coil assembly pair 301, 302 are separated fromeach other by a first gap 304. The first parallel primary coil assemblypair 301, 302 have respective boresights 307 and 308 separated by adistance 309. The second parallel primary coil assembly pair 313, 314are separated from each other by the first gap 304. The second parallelprimary coil assembly pair 313, 314 have respective boresights 315, 316separated by the distance 309. The respective pairs of parallel primarycoil assembly pairs are aligned rectilinearly and separated by a secondgap 318, whereby the respective boresights 308, 315 and 309, 316 areseparated by a second distance 317 left-right in the direction ofmovement 310 of the vehicle to be charged. The 2×2 cluster 312 can becharacterized as 2 side-by-side pairs, 2 diagonal pairs, and even as 2front-to-back pairs.

Additional, neighboring primary assemblies (2-to-2n) can be installed toextend the modular cluster shown in FIG. 3C by adding pairs in parallelto either side of the vehicle chassis centerline 303. Adjacent primaryassemblies are the nearest neighbor or nearest neighbors (all adjoining)in a modular cluster of primary assemblies. Non-adjacent primaryassemblies in a modular cluster are defined as neighboring. With the 2×2(and the larger 2×n, n>2) cluster pairing between primary coilassemblies, it becomes possible to use side-by-side (parallel to eitherside of the vehicle mid-line), diagonal, or front-to-back (both on thesame side of the vehicle midline) cluster pairings.

A cluster of primary assemblies (including single primary assembly orcluster of primary assemblies) may also be called a wireless chargepoint. A geographically grouped set of wireless charge points undercommon control is referred to as a wireless charging station. Largegroupings of wireless charge points under common control may alsodefined as wireless charging depots or wireless charging facilities.

A commercially deployed 200 kW system (4 primary coil assemblies at 50kW each with a center frequency of 20 kHz) had a 101.6 mm separationbetween neighboring primary coil assemblies. A later, also commerciallydeployed, 300 kW system (4 primary coil assemblies at 75 kW each with acenter frequency of 85 kHz) had a 75 mm separation between neighboringprimary coil assemblies. The closer spacing of the primary coilassemblies (and matched secondaries) can be adjusted for mechanical andinstallation considerations with a minimum spacing maintained to reduceinterference in misalignment situations and thus decrease overallsensitivity to misalignment between the primary and secondary coilassembly duos.

When the inductively coupled, wireless power transfer system is active,magnetic flux is produced by alternating current in the primary andsecondary coils. In the region surrounding the coils, the distributionof this magnetic flux is very well approximated by the equations formagnetic field of a dipole source located at the magnetic center of eachcoil. This field has a generally toroidal (donut) shape, with magneticflux directed in the poloidal direction (looping around through thedonut hole). As with any magnetic dipole source, field strength(equivalently flux density) drops off with the cube of distance (1/r³)from the dipole.

In one working 200 kW embodiment, the primary coil assemblies were each902 mm long and 902 mm wide. In a second working 300 kW embodiment, theprimary coil assemblies were each 725 mm long and 675 mm wide.

FIG. 4

FIG. 4 illustrates the contours of the constant magnetic flux densitycreated by a single, large primary coil assembly 401 plotted on aCartesian coordinate system with both axes showing distance (in meters)from the center of the primary coil assembly 401 during a chargingsession. This is a worst-case model since no shielding from theelectrical vehicle body is assumed.

The magnetic fields in FIG. 4 were modeled using finite element method(FEM) calculations to determine the magnetic flux density produced byconductive coils in the presence of other conductive materials (sourceof eddy currents) and magnetic materials.

When actively transferring power to the secondary coil assembly (notshown), the total magnetic flux density decreases as the distance fromthe center of the primary coil assembly 401 increases. When activelytransferring power to the secondary coil assembly (not shown), the totalmagnetic flux density decreases as the distance from the center of theprimary coil assembly 401 increases. Immediately surrounding the primarycoil assembly 401, the first contour line 404 denotes a constantmagnetic flux density of 316 μT (microteslas). The second contour line405 shows the constant magnetic flux density of 100 μT. The thirdcontour 406 shows the constant magnetic flux density of 31.6 μT. Thefourth contour 407 shows the constant magnetic flux density of 10 μT.The fifth contour 408 shows the constant magnetic flux density of 3.16μT. The sixth contour 409 shows the constant magnetic flux density of 1μT.

Recent proposed exposure rules for safe magnetic field exposure limitsinclude those from the independent non-profit group, the InternationalCommission on Non-Ionizing Radiation Protection (ICNIRP) and those fromthe technical professional engineering and standards association, theInstitute of Electrical and Electronics Engineers (IEEE). The UnitedStates Federal Communications Commission is investigating if newlimitations on magnetic exposure are necessary for Wireless PowerTransfer in Docket ET 19-226, “Targeted Changes to the Commission RulesRegarding Human Exposure to Radiofrequency Electromagnetic Fields.”

The suggested ICNIRP limit (from “Guidelines for limiting exposure toelectromagnetic fields (100 kHz to 300 GHz), Health Phys 118; March2020”) is 27 μT (very close to the 31.6 μT contour), while the relevantIEEE (from: “IEEE C95.1-2019-IEEE Standard for Safety Levels withRespect to Human Exposure to Electric, Magnetic, and ElectromagneticFields, 0 Hz to 300 GHz”) limit is 200 μT (between the 316 μT and 31.6μT contours) for the nominal 85 kilohertz magnetic charging signal.These contours are all within the typical vehicle width 402 centeredaround the primary coil assembly 401.

FIG. 5A

FIG. 5A illustrates the contours of constant magnetic flux densitycreated by a pair of modular in-line primary coil assemblies 501 and 502plotted on a Cartesian coordinate system with both axes showing distance(in meters) from the center point within the gap between the pair ofprimary coil assemblies 501 and 502 during an in-phase charging session.In this case, the pair of modular primary coil assemblies 501 and 502are powered from a common source and emit substantially identicalamplitude, frequency, and phased magnetic signals as set by themagnetics controller (not shown). In this example, the modular primarycoil assemblies 501 and 502 are placed in a tessellation following acongruent rectilinear grid pattern.

The additive magnetic flux density is shown by contours of constantmagnetic flux density. The first contour 505 shows the 316 μT constantmagnetic flux density. The second contour 506 shows the 100 μT constantmagnetic flux density. The third contour 507 shows the 31.6 μT constantmagnetic flux density. The fourth contour 508 shows the 10 μT constantmagnetic flux density. The fifth contour 509 shows the 3.16 μT constantmagnetic flux density. The sixth contour 510 shows the 1 μT constantmagnetic flux density.

A nominal width 503 of an automobile (1.8 meters) and a nominal length504 are drawn for illustration of a specific embodiment. As illustrated,the modular paired primary coil assembly shown in FIG. 5A is well suitedfor use in automotive charging. By placing the secondary coilassembly(s) on the underside of the vehicle, passengers and bystandersgain both shielding of magnetic flux and an exclusion zone onlyenterable by crawling under the vehicle. When inactive, magneticcharging signal exists, but low power inductive communications signalsmay.

The design of cars, trucks, buses, and other road-based vehicles followa consistent design where the length exceeds the width of the vehicle.Compared to the generally oval pattern of fields (versus the circularfields of a single primary coil assembly (see FIG. 1)), the 1×2 coilassembly of FIG. 5A takes advantage of both additional shielding fromthe metallic automobile body and the exclusion area provided by the autobody, frame, and wheels.

For every served EV, a set of individual secondary coil assemblies ispermanently associated with each vehicle. Information on the frequencyresponse for each secondary coil assembly can be maintained either bythe vehicle or at a central (landside) repository. By adjusting thecharging frequency for each primary coil assembly in each pair,discrepancies in frequency response (e.g., created by differingmanufacturers, makes, models of secondary coil assemblies) can beminimized. Since the pair at the new frequency would still beout-of-phase, substantial cancellation of magnetic flux is realized atthe cost of reduced efficiency.

FIG. 5B

FIG. 5B illustrates the contours of constant magnetic flux densitycreated by a pair of modular in-line primary coil assemblies 501 and 502plotted on a Cartesian coordinate system with both axes showing distance(in meters) from the center point within the gap between the pair ofprimary coil assemblies 501 and 502 during an out-of-phase chargingsession. In this example, the modular primary coil assemblies 501 and502 are placed in a tessellation following a congruent rectilinear gridpattern. In this case, the pair of modular primary coil assemblies 501and 502 are powered from multiple sources and produce substantiallyidentical magnetic charging signals in terms of determined amplitude andfrequency; however, the phase difference between the magnetic chargingsignals has been set to approximately 180°. As used in this context,“approximately” means ±10°.

The resultant additive magnetic flux density for the two chargingsignals is shown by the contour lines. The first contour 508 shows the316 μT constant magnetic flux density. The second contour 509 shows the100 μT constant magnetic flux density. The third contour 510 shows the31.6 μT constant magnetic flux density. The fourth contour 511 shows the10 μT constant magnetic flux density. The fifth contour 512 shows the3.16 μT constant magnetic flux density. The sixth contour 513 shows the1 μT constant magnetic flux density.

A nominal width 503 of an automobile (1.8 meters) and a nominal length504 are drawn for illustration of a specific embodiment. As illustrated,the modular paired primary coil assembly shown in FIG. 5B is well suitedfor use in automotive charging. By placing the secondary coilassembly(s) on the underside of the vehicle, passengers and bystandersgain both shielding of magnetic flux and an exclusion zone onlyenterable by crawling under the vehicle. When inactive, no magneticcharging signal exists.

FIG. 5C

FIG. 5C topographically illustrates the contours of constant magneticflux density created by a side-by-side pair of modular primary coilassemblies 501 and 502 plotted on a Cartesian coordinate system withboth axes showing distance (in meters) from the center point within thegap between the pair of primary coil assemblies 501 and 502 during anout-of-phase charging session. In this example, the modular primary coilassemblies 501 and 502 are placed in a tessellation following acongruent rectilinear grid pattern. In this case, the pair of modularprimary coil assembly duos 501 and 502 are powered from multiple sourcesand produce substantially identical magnetic charging signals in termsof determined amplitude and frequency; however, the phase differencebetween the magnetic charging signals has been set to approximately180°. The resultant additive magnetic flux density for the two chargingsignals is shown by the contour lines and is the same as in theembodiment of FIG. 5B except rotated 90 degrees.

The resultant additive magnetic flux density for the two chargingsignals is shown by the contour lines. The first contour 505 shows the316 μT constant magnetic flux density. The second contour 506 shows the100 μT constant magnetic flux density. The third contour 507 shows the31.6 μT constant magnetic flux density. The fourth contour 507 shows the31.6 μT constant magnetic flux density. The fifth contour 512 shows the1 μT constant magnetic flux density.

A nominal width 503 of an automobile (1.8 meters) and a nominal length504 are drawn for illustration of a specific embodiment. As illustrated,the 2×1 side-by-side configuration of modular paired primary coilassembly cluster shown in FIG. 5C is less well suited for use inautomotive charging than the 1×2 in-line configuration shown in FIG. 5Bdue to the larger area of magnetic flux outside the exclusion zoneformed by the car chassis (when placing the secondary coil assembly(s)on the underside of the vehicle as in this embodiment).

Since cars, trucks, buses, and other road-based vehicles follow aconsistent design where the length exceeds the width of the vehicle andvehicle width is limited by roadway lane width, the geometric shaping ofthe contours of constant magnetic flux density can better be affected bythe additional shielding provided by the metallic automobile body. It isnoted that the exclusion area around the primary coil assembliesprovided by the auto body, frame, and wheels can further limit potentialEMF exposure.

FIG. 6A

FIG. 6A illustrates a modular cluster of four primary coil assembliesarranged in a 2×2 cluster. Given the size of the individual primary coilassemblies, this geometric arrangement is well suited for installationunder a van, truck, trailer, or bus chassis. In FIG. 6A, each of theprimary coil assemblies are powered from a common source and sharetransmission frequency, phase, and power levels. In this example, themodular primary coil assemblies 601, 602, 603, and 604 are placed in atessellation following a congruent rectilinear grid pattern.

The additive magnetic flux density during an in-phase charging sessionis shown by the contours of constant magnetic flux density plotted on aCartesian coordinate system with the origin placed at the center of the2×2 cluster of primary coil assemblies. The first contour 607 shows the100 μT constant magnetic flux density. The second contour 608 shows the31.6 μT constant magnetic flux density. The third contour 609 shows the10 μT constant magnetic flux density. The fourth contour 610 shows the3.16 μT constant magnetic flux density. The fifth contour 611 shows the1 μT constant magnetic flux density.

In terms of human exposure, this scenario with all four primary coilassemblies 601, 602, 603, and 604 transmitting in the same frequency andphase shows the worst case of magnetic flux density. As can be seen fromthe nominal automobile width 605 and length 606, the 4×4 cluster isunlikely to be installed under an automobile having such dimensions.However, larger vehicles such as a bus (nominal chassis width 2.6meters) would provide additional overlap and therefore shielding ofpassengers and bystanders from elevated magnetic flux density.

FIG. 6B

FIG. 6B illustrates a modular cluster of four primary coil assembliesarranged in a 2×2 cluster. In this example, the modular primary coilassemblies 601, 602, 603, and 604 are placed in a tessellation followinga congruent rectilinear grid pattern. Also, in this example, the primarycoil assemblies are segregated into a first pair 601 and 602 and asecond pair 603 and 604 with each pair powered from a separate source orindividually powered, but with each pair sharing the same transmissionfrequency and power levels but with a set phase difference (e.g., 180°)between the side-by-side paired primary coil assemblies.

As discussed previously, the phase difference between paired primarycoil assemblies during an out-of-phase charging session results indestructive interference of the transmitted magnetic charging signals.The additive magnetic flux density is shown by the contours of constantmagnetic flux density plotted on a Cartesian coordinate system with theorigin placed at the center of the 2×2 cluster of primary coilassemblies. The first contour 614 shows the 100 μT constant magneticflux density. The second contour 615 shows the 31.6 μT constant magneticflux density. The third contour 616 shows the 10 μT constant magneticflux density. The fourth contour 617 shows the 3.16 μT constant magneticflux density. The fifth contour 618 shows the 1 μT constant magneticflux density.

The resultant shape of the magnetic field (as shown by the 1 μT contour618) is not only reduced in area but also is preferentially lowered tothe EV sides where passenger ingress and egress is expected. Largervehicles such as a bus (nominal chassis width 2.6 meters) would provideadditional overlap and therefore shielding of passengers and bystandersfrom elevated magnetic flux density.

FIG. 6C

FIG. 6C illustrates a modular cluster of four primary coil assembliesarranged in a 2×2 cluster. In this example, the modular primary coilassemblies 601, 602, 603, and 604 are placed in a tessellation followinga congruent rectilinear grid pattern.

In this embodiment, the primary coil assemblies are segregated into adiagonal first pair 601 and 603 and a diagonal second pair 602 and 604with each pair powered from a separate source or individually powered,but with each pair sharing the same power levels with a set phasedifference (e.g., ˜180°) between pair members. To compensate for afrequency offset in a secondary assembly (not shown), the first diagonalprimary coil pair 601 and 603 is set to transmit at a differentfrequency than the second diagonal primary coil pair 602 and 604 duringthe out-of-phase charging session.

The first contour 614 shows the 100 μT constant magnetic flux density.The second contour 615 shows the 31.6 μT constant magnetic flux density.The third contour 616 shows the 10 μT constant magnetic flux density.The fourth contour 617 shows the 3.16 μT constant magnetic flux density.The fifth contour 618 shows the 1 μT constant magnetic flux density.

The resultant pattern of magnetic flux density contours has a roundedsquare shape but still provides an advantage in flux density reductionover the nominal pattern and area shown in FIG. 6A. The shaping of thefield pattern is also advantageous in that the reduction to the sides ofthe cluster and thus sides of the EV is pronounced.

FIG. 6D

FIG. 6D illustrates a modular cluster of four primary coil assembliesarranged in a 2×2 cluster. In this example, the modular primary coilassemblies 601, 602, 603, and 604 are placed in a tessellation followinga congruent rectilinear grid pattern. However, this example, the primarycoil assemblies are segregated into a side-by-side first pair 601 and604 and a side-by-side second pair 602 and 603 with each pair poweredfrom a separate source or individually powered, but with each pairsharing the same transmission frequency and power levels but with a setphase difference (e.g., 180°) between the side-by-side paired first andsecond primary coil assemblies during an out-of-phase charging session.

In FIG. 6D, the first contour 614 shows the 100 μT constant magneticflux density. The second contour 615 shows the 31.6 μT constant magneticflux density. The third contour 616 shows the 10 μT constant magneticflux density. The fourth contour 617 shows the 3.16 μT constant magneticflux density. The fifth contour 618 shows the 1 μT constant magneticflux density.

As can be seen in comparison with FIG. 6B (side-by-side pairing ofout-of-phase primary coil assemblies) and FIG. 6C (diagonal pairing ofout-of-phase primary coil assemblies), the side-by-side configurationdoes not reduce the magnetic flux density as well as the diagonalconfiguration does.

FIG. 7A

FIG. 7A illustrates a modular cluster of three primary coil assembliesarranged in a 1×3 cluster. This geometric arrangement is intended forinstallation under a van, truck, trailer, or bus chassis. In thisexample, the modular primary coil assemblies 701, 702, and 703 areplaced in a tessellation following a congruent rectilinear grid pattern.

The additive magnetic flux density during an in-phase charging sessionis shown by the contours of constant magnetic flux density plotted on aCartesian coordinate system with the origin placed at the center of thecenter primary coil assembly 702. The first contour 706 shows the 316 μTconstant magnetic flux density. The second contour 707 shows the 100 μTconstant magnetic flux density. The third contour 708 shows the 31.6 μTconstant magnetic flux density. The fourth contour 709 shows the 10 μTconstant magnetic flux density. The fifth contour 710 shows the 3.16 μTconstant magnetic flux density. The sixth contour 711 shows the 1 μTconstant magnetic flux density.

The oval patterns of the contours of constant magnetic flux density arewell suited for use in a WPT system where reduction in EMF produced isdesired since arrangement of the cluster along the centerline of the EVproduces maximum isolation and shielding of bystanders.

FIG. 7B

FIG. 7B illustrates a modular cluster of three primary coil assembliesarranged in a 1×3 cluster. Given the size of the individual primary coilassemblies, this geometric arrangement is well suited for installationunder a van, truck, trailer, or bus chassis. In this example, themodular primary coil assemblies 701, 702, and 703 are placed in a row(the same tessellation following a congruent rectilinear grid pattern isused). The Cartesian plane is centered on the midpoint of the centerprimary coil assembly 702.

As discussed previously, the phase difference between paired primarycoil assemblies results in destructive interference of the transmittedmagnetic charging signals during an out-of-phase charging session. Withthree primary coil assemblies in the cluster, a modified version ofpairing may be required. By setting the first primary coil assembly 701and the third primary coil assembly 703 to transmit the same chargingsignal power, frequency, and phase, and then setting the middle primarycoil assembly 702 to transmit a charging signal of the same power andfrequency, but out of phase with first primary coil assembly 701 and thethird primary coil assembly 703, a substantial reduction in the magneticflux density can be achieved.

The additive magnetic flux density is shown by the contours of constantmagnetic flux density plotted on a Cartesian coordinate system with theorigin placed at the center of the center primary coil assembly 702. Thefirst contour 713 shows the 316 μT constant magnetic flux density. Thesecond contour 714 shows the 100 μT constant magnetic flux density. Thethird contour 715 shows the 31.6 μT constant magnetic flux density. Thefourth contour 716 shows the 10 μT constant magnetic flux density. Thefifth contour 717 shows the 3.16 μT constant magnetic flux density. Thesixth contour 718 shows the 1 μT constant magnetic flux density.

The reduction of the field as shown by the magnetic field contoursversus the nominal FIG. 7A is substantial. The shaping of the field,where the contours are much reduced to the EV sides, is alsoadvantageous.

FIG. 7C

FIG. 7C illustrates a modular cluster of three primary coil assembliesarranged in a 1×3 cluster. In this example, the modular primary coilassemblies 701, 702, and 703 are placed in a row (the same tessellationfollowing a congruent rectilinear grid pattern is used). The Cartesianplane is centered on the midpoint of the center primary coil assembly702.

In addition to the setting the first primary coil assembly 701 and thethird primary coil assembly 703 to transmit the same charging signalpower, frequency and phase, and then setting the middle primary coilassembly 702 to transmit a charging signal of the same frequency, butout-of-phase (e.g., 180°) with first primary coil assembly 701 and thethird primary coil assembly 703, the power of the middle primary coilassembly 702 can be increased (alternately, the power of the chargingsignal for first primary coil assembly 701 and the third primary coilassembly 703 can be reduced) to create a greater reduction in themagnetic flux density than phase adjustment alone can achieve.

In this example of an out-of-phase charging session with power control,the outer primary coils 701 and 703 are set to carry 70% of the currentof the middle primary coil 702. Power levels are thus 50% in the outercoils 701 and 703 and 50% in the middle coil 702. The first contour 721shows the 100 μT constant magnetic flux density. The second contour 722shows the 31.6 μT constant magnetic flux density. The third contour 723shows the 10 μT constant magnetic flux density. The fourth contour 724shows the 3.16 μT constant magnetic flux density. The fifth contour 725shows the 1 μT constant magnetic flux density.

The area of the magnetic field (as shown by the magnetic flux densitycontours) is reduced by the power control. Adjustments to the powercontrol levels can further be used to shape the magnetic flux density tobest fit the EV chassis shielding and exclusion area.

FIG. 7D

FIG. 7D illustrates the effective magnetic flux density reduction whenusing a 1×3 primary coil assembly cluster with virtual pairwisecancellation and power control during an out-of-phase charging session.The percentage of magnetic cancellation versus the current differencecan be obtained when the current in the outer two coils is 180 degreesout of phase with the center coil and the outer coil current is variedas a proportion of center coil current. In FIG. 7D, the X-axis shows thecurrent ratio (in percentage terms) between the inner and outer coilsets and the Y-axis shows the proportion of flux density cancelled whenone coil set (e.g., the outer coils) carries current that isapproximately 180 degrees out-of-phase with the current carried by theother set (e.g., the inner coil).

Curve 726 represents the maximum of the flux density cancellationachievable along a line beside the couplers corresponding to a typicalvehicle edge (1.3 m). Curve 726 has three regions, 729, 730, and 731. Inregion 729, the current in the outer sets is too low to allow formaximum cancellation. In region 730, the current in the outer sets is atan appropriate level to allow for maximum cancellation. In region 731,the current in the outer sets is too high to allow for maximumcancellation. Operation in regions 730 or 731 confers benefits ofreduced magnetic flux while tailoring power delivered to situationalneed.

Curve 727 represents the minimum (worst-case) of the flux densitycancellation achievable along a line beside the couplers correspondingto a typical vehicle edge (1.3 m). Curve 727 has two regions 732 and733, and one maximum at 728. In region 732, the minimum cancellationincreases as current in the outer sets increases. In region 733, theminimum cancellation decreases as current in the outer sets increases.These regions surround a point where the minimum cancellation is at itsgreatest. Operation approximate this point ensures the most significantoverall reduction in fields as it is also in region 730 for curve 726which has the best maximum cancellation.

FIG. 8A

FIG. 8A illustrates a cluster of six modular primary coil assembliesarranged in a 2×3 cluster during an in-phase charging session. Given thesize of the individual primary coil assemblies, this geometricarrangement is well suited for installation under larger vehicles suchas a truck, a trailer, or a bus. In this example, the modular primarycoil assemblies 801, 802, and 803 are placed in a first row and themodular primary coil assemblies 804, 805, and 806 are placed in a secondrow following the same tessellation in congruent rectilinear gridpattern. The Cartesian plane map is centered on the midpoint between thecenter pair of primary coil assemblies 802 and 805.

The first contour 807 shows the 316 μT constant magnetic flux density.The second contour 808 shows the 100 μT constant magnetic flux density.The third contour 809 shows the 31.6 μT constant magnetic flux density.The fourth contour 810 shows the 3.16 μT constant magnetic flux density.The fifth contour 811 shows the 1 μT constant magnetic flux density.

FIG. 8B

FIG. 8B illustrates a modular cluster of six primary coil assembliesarranged in a 2×3 cluster. This geometric arrangement is intended forinstallation under a larger truck, trailer, or bus chassis. In thisexample, the modular primary coil assemblies 801, 802, 803, 804, 805,and 806 are placed in a tessellation following a congruent rectilineargrid pattern of 2 rows by 3 columns (2×3) along the length of thevehicle.

In FIG. 8B, magnetic energy is transmitted both with offsets of both 0degrees and 180 degrees phase shifts by the first pair 801 and 804, thesecond pair 802 and 805, and the third pair 803 and 806. This diagonalpattern allows each primary and secondary coil assembly duo to beneighbored only by duos of the opposite phase-offset during a chargingsession.

The additive magnetic flux density is shown by the contours of constantmagnetic flux density plotted on a Cartesian coordinate system with theorigin placed at the center of the cluster at the midpoint betweenprimary coil assembly 802 and primary coil assembly 805. The firstcontour 814 shows the 316 μT constant magnetic flux density. The secondcontour 815 shows the 100 μT constant magnetic flux density. The thirdcontour 816 shows the 31.6 μT constant magnetic flux density. The fourthcontour 817 shows the 10 μT constant magnetic flux density. The fifthcontour 818 shows the 3.16 μT constant magnetic flux density. The sixthcontour 819 shows the 1 μT constant magnetic flux density.

As can be seen by the contours, the magnetic flux density issubstantially decreased at the 1 meter, 2 meter and 3 meter rangesversus the case where all six 6 primary coil assemblies are transmittingat the same phase (as shown in FIG. 8A). It is also noted that the shapeof the magnetic field as described by the contours of magnetic fluxdensity shown in FIG. 8B are substantially, favorably reduceddirectionally to the side. Assuming a deployment of secondary coilassemblies along the midline of the vehicle, the chassis of the vehiclewould provide both shielding and human exclusion area of magnetic fluxfor this configuration.

FIG. 8C

In FIG. 8C, magnetic energy is transmitted both at 0 degrees and 180degrees phase shifts by the first pair 801 and 804, the second pair 802and 805, and the third pair 803 and 806 during a side-by-side pairwiseout-of-phase charging session. This pattern sets up a side-to-sidemagnetic flux cancellation scheme.

The additive magnetic flux density is shown by the contours of constantmagnetic flux density plotted on a Cartesian coordinate system with theorigin placed at the center of the cluster at the midpoint betweenprimary coil assembly 802 and primary coil assembly 805. The firstcontour 820 shows the 316 μT constant magnetic flux density. The secondcontour 821 shows the 100 μT constant magnetic flux density. The thirdcontour 822 shows the 31.6 μT constant magnetic flux density. The fourthcontour 823 shows the 10 μT constant magnetic flux density. The fifthcontour 824 shows the 3.16 μT constant magnetic flux density. The sixthcontour 825 shows the 1 μT constant magnetic flux density.

The side-by-side pairwise cancellation results in equivalent magneticflux density with both greater area and a less advantageous shaping. Theincrease in range of the equivalent magnetic flux density to the EVsides is contrary to the goal of reducing exposure to bystanders andentering or departing passengers.

FIG. 9

FIG. 9 illustrates two views of a generic electric or hybrid sedan ofthe type commonly used as a taxi. The side view 901 shows a samplesingle, vehicle mounted secondary coil assembly 903. The secondary coilassembly is also known as the receiver or vehicle assembly (VA).

The top see-through view 902 shows the placement of the secondary coilassembly 904 in the middle of the sedan chassis side-to-side andimmediately behind the front wheels to lessen the chance of damage tothe coil assembly from uneven road surfaces. The exclusion zone 905shows the relatively inaccessible area created by the periphery of thevehicle's undercarriage. In sample embodiments, the magnetic fieldcreated while charging is advantageously shaped and limited to bepredominately within the exclusion zone 905.

FIG. 10

FIG. 10 illustrates two views of a generic electric or hybrid van of thetype commonly used as a transit vehicle. The side view 1001 illustratesa positioning option for the 1×2 pair of vehicle mounted secondary coilassemblies 1003 and 1004. The top see-through view 1002 shows afavorable position for mounting the first 1005 and second 1006 receiveralong the mid-line of the chassis side to side and close behind thefront wheels to lessen the chance of damage to the coil assemblies fromuneven road surfaces. The exclusion zone 1007 shows the relativelyinaccessible area created by the periphery of the vehicle'sundercarriage. The magnetic field created while charging isadvantageously shaped and limited to be predominately within theexclusion zone 1007.

FIG. 11

FIG. 11 illustrates two views of a generic electric or hybrid transitbus. The side view 1101 illustrates a positioning option for a 2×2cluster 1103 of vehicle mounted secondary coil assemblies. The topsee-through view 1102 shows a favorable position for mounting thesecondary cluster 1104 along the mid-line of the chassis side-to-sideand close behind the front wheels to lessen the chance of damage to thecoil assemblies from uneven road surfaces. The exclusion zone 1105 showsthe relatively inaccessible area created by the periphery of thevehicle's undercarriage. The magnetic field created while charging isadvantageously shaped and limited to be predominately within theexclusion zone 1105.

FIG. 12

FIG. 12 illustrates an example of a secondary or receiver cluster on ageneric electric or hybrid bus in side 1201 and see-through top 1202views. The side view 2101 illustrates a positioning option for a 2-by-3(2×3) cluster 1203 of vehicle-mounted secondary coil assemblies. The topsee-through view 1202 shows an exemplary position for mounting theexample 2×3 secondary cluster 1204 along the mid-line of the undersideof the bus chassis side-to-side and close behind the front wheels tolessen the chance of damage to the coil assemblies from uneven roadsurfaces. The exclusion zone 1205 shows the relatively inaccessible areacreated by the periphery of the vehicle's undercarriage. The magneticfield created while charging is advantageously shaped and limited to bepredominately within the exclusion zone 1205. As noted above, onlymagnetic flux density below a threshold is allowable outside theexclusion zone.

FIGS. 9-12 illustrate the engineering trade-off between mechanicalconsiderations (lessening the probability of damage from curbs,speed-bumps) with the use of the metallic chassis body as a magneticshield to further reduce emissions. As the vehicle chassis varies andthe number of modular secondary assemblies vary, the ability to shapethe magnetic field (using destructive cancellation as tuned via thesupplied power, frequency, phase, and secondary assembly layout) tominimize exposure to magnetic flux increases in utility.

In FIGS. 9-12, the exclusion zone perimeter is shown as coincident withthe outline of the metallic vehicle body or undercarriage. Inalternative embodiments, the exclusion zone may be a smaller portion ora larger expansion of the area outlined by the vehicle periphery and mayinclude multiple areas corresponding to different levels of magneticflux density. The smaller area may, for instance, be bounded by thesensor coverage of a foreign object detection (FOD) system or livingobject detection system (LOD). A larger area may be defined by akeep-away zone delineated by physical barriers or markings. A FOD or LODsystem sensor coverage area may also be used to establish an exclusionzone larger than the vehicle outline. These smaller and larger exclusionzones may then be used for attaining a desirable shaping for thegenerated area of magnetic flux density above a threshold. Alternately,the shaping of the generated area of magnetic field may be used foradjustment of the exclusion area size and borders.

FIG. 13

FIG. 13 illustrates a plot of the cancellation of magnetic flux densityversus diagonal pairwise phase differences for a representative 2×2cluster (4 primary and secondary coil assembly duos, paired diagonallyas in FIG. 6B). The X-axis indicates the phase angle between the pairedsets. The Y-axis indicates the amount of cancellation of flux density at1.3 meters (corresponding to the edge of a typical transit or schoolbus) from the center of the cluster. The two lines 1301, 1302 indicatedifferent magnitudes of flux density cancellation at different phaseangles. The first line 1301 shows the maximum amount of flux densitycancellation that can be achieved along the 1.3 m radius circle centeredon the cluster. This maximum cancellation is generally along the axes ofthe grid formed by the 2×2 cluster. The second line 1302 shows theminimum amount of flux density cancellation that can be achieved alongthe 1.3 m radius circle centered on the cluster. This minimumcancellation is generally along the diagonals of the grid formed by the2×2 cluster.

While all phase offsets show some cancellation for both the best 1301and worst 1302 cases, the worst case 1302 line shows that in the firstregion 1303 which extends from 0 to 25 degrees of phase offset betweencoordinated primary assembly pairs, essentially no cancellation isachieved (<1%). Therefore, phase offsets in the second region 1304extending from 25 degrees to 180 degrees are preferred.

FIG. 14

FIG. 14 illustrates a high-power wireless power transfer system that maybe adapted to incorporate the modular coil assemblies described hereinfor electrical vehicles with battery storage. Battery storage includeswet cell, dry cell, and solid-state batteries as well as capacitivestorage and reversable fuel cells and combinations thereof (i.e.,hybrid) energy storage.

In this system, the ground-side electronics 1401 provides a conditionedpower signal to the primary coil assembly 1402. As preferred in highpower systems, the primary coil assembly 1402 may have a balancedseries-series configuration having primary coil windings 1403 andmatched capacitors 1404 and 1405.

Across an air-gap 1410, the secondary coil assembly 1406 is used toreceive the magnetic signal generated by the primary coil assembly 1402.The secondary coil assembly 1406 also may have the balancedseries-series configuration with the secondary coil windings 1407 andmatched capacitors 1408 and 1409. The AC power level, frequency, andphase (i.e., the AC signal data) generated by the secondary coilassembly 1406 is measured by a sensor 1411 that reports thesemeasurements via digital datalink 1412 to the active rectifiercontroller (ARC) 1413. The ARC 1413 uses the AC signal data topredictively model the signal to determine zero crossings to optimizethe active rectification. Rectification control signals are passed viacontrol links 1417 to the active rectifier 1416 which takes the ACsignal inputs 1415 and converts them to a DC power output 1419.Temperature sensors (now shown) in the rectifier module use digitaldatalinks 1418 to report to the ARC 1413. The power conditioner 1420takes the DC output 1419 of the rectifier 1416 and removes ripple andnoise at filter 1421 to charge the battery pack 1424. The conditioned DCsignal characteristics are monitored by a sensor 1422 and reported backto the ARC 1413 via digital datalink 1423.

A landside data repository 1426, embodied as a single generic computeror cluster of computers and software database or constructed as adistributed embodiment with multiple geographically diverse sites eachwith computing resources and databases, may maintain charging profilesof default and historical measurements for each secondary coil assemblyinstalled on a vehicle. The repository 1426 contains performance data,including frequency response and charging models, which can be requestedover a data network 1427 by the charging site controller 1428 (a genericcomputer or computer cluster running site management software anddatabase software) for setting charging session parameters when avehicle is being charged.

These charging session parameters may include magnetic signalcharacteristics for each primary coil assembly or primary coil assemblypair (e.g. instantaneous power level during charging session, basesignal frequency, frequency drift, signal phase offset, and nominalcoil-to-coil gap) based on the aligned secondary coil (or pairs ofaligned primary and secondary) and local conditions such as poweravailability, environmental factors (e.g. temperature) and installedprimary coil assembly conditions (e.g. internal temperature(s), usagefactors, number of coils per primary, number of turns per primary,surface mounted or flush mounted primary coil assembly(s)).

The charging session parameters may also include the charger profile ofthe primary coil assembly or primary coil assembly pair of the typeillustrated in Table 1:

TABLE 1 Charger Profile Primary coil identifiers Flush mount or raisedmount Number of Turns per Primary coil Make, model, manufacturerAutonomous Alignment capability Min. /Max. current and voltage supportCommunications protocols available Communications bandwidth

Automotive charging related data may also be stored in the datarepository 1426. This data may include battery aging information (e.g.,charging-time versus battery charge state for one or more chargingsessions) as well as the siting of the secondary coil assemblies on thechassis, and the EM shielding provided by the EV body.

Table 2 below provides a sample vehicle charging profile that may bestored in the data repository 1426 and/or stored on the vehicle side andcommunicated to the ground side charger during charging.

TABLE 2 Vehicle Charging Profile Per secondary coil frequency offsetSecondary Make, model, manufacturer Number of Secondary Coil AssembliesPositioning of Secondary Coil Assemblies BMS Make, model, manufacturerMin./Max. current and voltage support Health status per Secondary CoilTemperature limitations Assembly(s) Temperature readings Coolingavailably

Access to the vehicle charging profile and near real-time data gives theWPT, via the charging site controller 1428, the ability to reconfigureeach primary coil at session initiation and during charging sessionbased on data from the primary coil assembly sensors, as well asfeedback from secondary and/or load across the air gap 1410 via theinductive communications system (not shown).

Access to the charging site controller 1428 is via digital datalink 14291430 with each first primary and secondary coil assemblies 1431 andsecond primary and secondary coil assemblies 1432 having access to thesame profile information. The current developed by each primary andsecondary coil assembly 1431 1432 in the charging point is combined atthe positive battery terminal 1433 and negative battery terminal 1434and used to charge the vehicle battery pack 1424.

The first ARC 1413 and second ARC (not shown) reports both AC and DCpower characteristics to a networked controller 1414 for storage andreporting via digital datalinks 1435.

FIG. 15

FIG. 15 illustrates, at a high level, the electric vehicle systemsinvolved with automatic wireless charging in sample embodiments. Asillustrated, the electric vehicle 1500 is equipped with a secondaryvehicle coil assembly 1502 (in this case a single coil unit) thatreceives wireless charging from a primary ground coil assembly 1501. TheBattery Management System (BMS) 1509 is responsible for monitoring andmanagement of the battery pack 1504. Note that the term “battery pack”is used herein to depict a generic chemical energy storage system andcould be replaced, supplemented, or hybridized with other portableenergy storage systems (e.g., solid-state battery arrays, reversablefuel cells, ultra-capacitors). Based on algorithms, the BMS 1509 managesperformance and maximizes range and longevity by setting charge ratesand balancing individual cell (or cell bank) charging/discharging whilemonitoring charge levels and temperatures.

The BMS 1509 controls the charging session (and associated logistics,billing, and sensor reading) with messaging sent via the downlinkdatalink 1505 and uplink datalink 1506 supported by the inductivecommunications transceiver system provided by the secondary assembly1502. A data store of the BMS 1509 includes identity and authorizationinformation, battery voltage, and a maximum current level setting. TheBMS 1509 may, optionally, contain a local version or subset of themagnetic charging data profile for the vehicle and installed secondaryassembles. The wireless charging controller 1503 functions to translateand bridge the vehicle network and the inductive communicationstransceiver system via data link 1507. The BMS 1509 receives sensor datafrom the battery pack 1504 sent via wired or wireless datalink 1510,which may be, for example, implemented over a Controller Area Network(CAN) bus.

The secondary vehicle coil assembly 1502 delivers direct current to thebattery pack 1504 via a high-current bus 1508. In cases where thebattery pack 1504 is fully charged, current also may be diverted orshared with onboard systems of vehicle 1500, such as communications,entertainment, and environmental control while in the queue and alignedand in communications with the charge point's maximum current levelsetting.

FIG. 16

FIG. 16 illustrates the wireless charging signals and ranges used inautomatic wireless charging at a single charge point in sampleembodiments. For automatic charging, the ground primary assembly 1601,shown here as embedded to be flush with the surface of the pavement1602, is substantially aligned and in communication with the vehiclesecondary assembly 1603 during charging. In this example, the secondaryassembly 1603 is mounted on the underside of the vehicle chassis 1604.

Before the charging signal 1605 can be initiated, an uplink 1606 anddownlink 1607 data path are established using inductive communicationlinks using communication devices as described, for example, in U.S.Pat. No. 10,135,496, incorporated herein by reference. The inductivelinks 1606 and 1607 are power limited with approach range 1608 anddeparture range 1609 barely exceeding the size of the primary groundcoil assembly 1601 (approximately 500 millimeters). Additionalinformation on the alignment process can be found in U.S. Pat. No.10,814,729, entitled “Method and apparatus for the alignment of avehicle and charging coil prior to wireless charging;” U.S. Pat. No.10,193,400 entitled “Method of and apparatus for detecting coilalignment error in wireless inductive power transmission;” and U.S. Pat.No. 10,040,360 entitled “Method and apparatus for the alignment ofvehicles prior to wireless charging including a transmission line thatleaks a signal for alignment,” the contents of which are incorporatedherein by reference. Other embodiments with alternative short rangelocal area wireless networking technologies (e.g., Bluetooth, Zigbee,Wi-Fi) or longer range Wireless wide area network (WWAN) technologies(e.g., cellular technology such as LTE, Connected-Car wireless packetdata systems, Vehicle-to-Infrastructure (V2I), Vehicle-to-Everything(V2X)) may be used.

FIG. 17

FIG. 17 is a flowchart illustrating a method 1700 of charging anelectric vehicle in a sample embodiment. In the illustrated example, thecharging point is in Standby state 1701 until bi-directionalcommunications are initiated. The charging point may, while in thestandby state, emit an inductive communications beacon. Alternately, thecharging point may only begin to emit a beacon when the charging sitecontroller 1428 commands it due to reception of arrival information viaa radio communications system (e.g., Wireless Local Area Network (WLAN)or a Wide Area Radio Communication System (e.g., cellular packet radiosystems)) or another vehicle detection mechanism indicating that theelectric vehicle is approaching the charging point.

Bi-directional communications are started in the Initiate Comms state1702. To enter Initiate Comms state 1702, a bi-directionalcommunications link is set up, and authentication and authorization tocharge are established. While the Initiate Comms state 1702 may beentered prior to alignment of the primary coil assembly(s) with thesecondary coil assembly(s) and the Obtain Setup Data 1703 may begin oncea reliable bi-directional link is assured, the Obtain Profile state 1704will not commence until after alignment is complete.

Once bi-directional communications are initiated and established (andthus the presence of the EV to be charged is assured), charging sessionsetup data can pass between the EV's computer systems and landsideauthentication, authorization, and payment services. Either as part ofthis Obtain Setup Data state 1703 or as part of a discrete ObtainProfile state 1704, details about the EV's inductive chargingcapabilities are obtained. The Obtain Setup Data state 1703 may alsoinclude details on the vehicle's charging power-level requested.

The EV's charging profile can be obtained in several ways, based on theelection of the EV designer and operator. In one instance, the EV'scomputer systems (e.g., the Battery Management System (BMS), orAutomated Driving System (ADS)) contain the charging profile fordownload. In another instance, the charging profile is downloaded from alandside data repository using the EV information obtained early in theObtain Setup Data state 1703. Alternately, a general EVmake-model-manufacturer charging profile may be used (obtained from theEV, landside repository, or local cache) or a default charging profilebased on the number and layout of the EV secondary coil assembliesdiscovered can be used if no charging profile or EVmake-model-manufacturer information is available.

Once the charging profile is obtained in the Obtain Profile state 1704,the Set Charging Parameters state 1705 is entered. In the Set ChargingParameters state 1705, the charging signal for each primary coilassembly is set in terms of frequency, amplitude, and phase. Theparameters for the charging signal are set to a charging signal having amagnetic field that is predominately within the exclusion zone based onthe obtained magnetics profile and the requested charging power level.

The charging point turns on the charging signal at the start of theInitiate Charging state 1706. Once charging is started, the Chargingstate 1707 is maintained until it is determined at 1708 that charging iscompleted or otherwise terminated. A normal completion event includesending of the session by the EV (e.g., battery full), termination by thesession by the charging site controller 1428 (e.g., pre-paymentauthorization level met) or by the primary or secondary coil assemblies(e.g., detection the EV has driven off the charging point). After anynormal charging session completion event, the charging point statereverts to Standby state 1701. An abnormal session termination event(e.g., overheating detected) is considered a fault and results inimmediate termination of the charging session 1707 with the chargingpoint set in a STOP state 1709 until the fault has been resolved.

Additional Embodiments Bi-directional

Since only the tightly coupled power-transferring coils are involved,bi-directional power transfer at reduced total magnetic flux is enabledfor either direction using the phase, frequency, and power controlpreviously described. The bi-directional power transfer may require theaddition of DC to AC conversion on the vehicle as well as AC-DC-AC orAC/AC conversion on the ground side to supply the local AC grid.

Mix and Match

With control over the inductive communications link and the frequency,power-level, and phase of the charging signal at each primary coilassembly, arbitrarily large grids can be constructed. For each chargingsession, a unique pattern of primary coil assemblies can be selected tosend power. In one example, a 3×3 grid of primary coil assemblies isconstructed. Using the vehicle profile to determine the number andplacement of secondaries on the EV, the EV can be maneuvered by thedriver or automated piloting via lane indicators or communicationsignals sent to the EV so that a set of primary coil assemblies will bealigned with the EV's secondary coil assemblies. The 3×3 example wouldbe capable of charging vehicles with 3×3 arrays of secondary coilassemblies, as well as those with 1×1, 1×2, 1×3, and 2×3 arrays wherethe appropriate subset of the 3×3 coil assembly on the ground side isactivated.

In certain cases, EVs can be charged from primary coil assemblies withsmaller arrays. For example, a 1×2 primary array could be used to chargean EV equipped 2×3 secondary array where the two primary coil assembliesalign with two of the six secondary coil assemblies.

In cases where an EV has one or more secondary coil assemblies isinoperative, a charging station can charge the EV using only thoseprimary coil assemblies that align to functional secondary coilassemblies.

In each circumstance, and optionally based on the magnetic chargingprofile of the EV, the frequency, phase, and power of the chargingsignal generated by the primary coil assemblies can be adjusted to limitmagnetic emissions.

Wide Area Balancing

The ability to control frequency, phase, and power for each of themodular primary coil assemblies not only in a single charge point (acluster of primary coil assemblies serving a single vehicle), but alsofor closely spaced deployments of multiple charge points (e.g., in adepot, parking lot, traffic queue or railyard).

A mapping of the maximum magnetic field (e.g., the magnetic fluxdensity) can be created from sensor readings at deployment or bymodeling. A model can be created or augmented using a real-time localsensor array of 1 or more discrete antennas that can be used to measureaggregate magnetic flux density originating from charge points or otherassociated electrical equipment.

The 3-dimensional aggregate magnetic flux density is calculated by aprocessor or obtained via sensors that have processing capabilities soas to function as means for identifying any additive ‘hot spots’ ofmagnetic flux densities. A series of best case, worst case models can begenerated by the identifying means. Similarly, ground level and headlevel models can be generated by the identifying means.

The power, phase, and frequency offsets then may be used to rebalancemagnetic charging signals to reduce or eliminate any areas of magneticflux densities above a desired safety/exposure threshold (e.g., anoperator defined fraction of the FCC Part 15, Part 18, IEEE C.95 orICNRIP thresholds).

FIG. 18

FIG. 18 graphically illustrates a charging station equipped with widearea magnetic flux management in a sample embodiment. The embodiment ofFIG. 18 provides magnetic field balancing through coordination ofmultiple modular wireless charging points. The charging station 1801includes a paved area 1802 and landscaping areas 1803. The landscapingareas 1803 can contain the power supplies (not shown) needed forpowering the wireless charging points and can by installation of berms,wire barriers, and walls help segregate and contain magnetic fluxgenerated by the charge points 1804 when in operation. Occupied chargepoints 1805, 1806, and 1807 generate magnetic flux while the inoperativecharge points 1804 are quiescent. To minimize areas of additive magneticflux density, predetermined models can be applied to adjust the phase ofthe in-operation charging points 1805, 1806, and 1807. One or moremagnetic antenna 1808 may be deployed to augment, monitor, or supplementthe wide-area magnetic flux mitigation scheme through destructiveinterference as described herein. In this embodiment, a single,centrally located monitoring antenna station 1808 is shown. Multipleantenna stations may be deployed as means to monitor the perimeter ofthe charging station, at known additive hot spots, or in areas withunprotected pedestrian traffic and to provide destructive interferencesignals as needed. The antenna stations may provide signals to therespective coil assemblies for adjusting the power, phase, and/orfrequency offsets of the coil assemblies in a vicinity of the additivehot spot of magnetic flux densities to balance charging signals from therespective coil assemblies to reduce magnetic flux densities at theadditive hot spot of magnetic flux densities.

CONCLUSION

Those skilled in the art will appreciate that the topology and circuitimplementation methodology described herein enable magnetic flux densityto be controlled in accordance with the dimensions and characteristicsof the vehicle on which the coil assembly is mounted.

The examples and figures used are descriptive of clusters ofgeometrically symmetric primary and secondary coil assemblies with coilsof each arranged in the same plane. Use of the same sizes and co-planarcoil deployments were used for ease of descriptions. Non-symmetriccoils, non-rectilinear grid placements and non-co-planar deployments canuse the principles and techniques described herein to manage productionof magnetic field but with potentially lower performance.

While various implementations have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. For example, any of the elements associated with the systemsand methods described above may employ any of the desired functionalityset forth hereinabove. Thus, the breadth and scope of a preferredimplementation should not be limited by any of the above-describedsample implementations.

As discussed herein, the logic, commands, or instructions that implementaspects of the methods described herein may be provided in a computingsystem including any number of form factors for the computing systemsuch as desktop or notebook personal computers, mobile devices such astablets, netbooks, and smartphones, client terminals and server-hostedmachine instances, and the like. Another embodiment discussed hereinincludes the incorporation of the techniques discussed herein into otherforms, including into other forms of programmed logic, hardwareconfigurations, or specialized components or modules, including anapparatus with respective means to perform the functions of suchtechniques. The respective algorithms used to implement the functions ofsuch techniques may include a sequence of some or all of the electronicoperations described herein, or other aspects depicted in theaccompanying drawings and detailed description below. Such systems andcomputer-readable media including instructions for implementing themethods described herein also constitute sample embodiments.

The monitoring and control functions of the active rectifier controller1413, the vehicle's current charging site controller 1428, and/orvehicle charging controller 1414 described herein may be implemented insoftware in one embodiment. The software may consist of computerexecutable instructions stored on computer readable media or computerreadable storage device such as one or more non-transitory memories orother type of hardware-based storage devices, either local or networked.Further, such functions correspond to modules, which may be software,hardware, firmware, or any combination thereof. Multiple functions maybe performed in one or more modules as desired, and the embodimentsdescribed are merely examples. The software may be executed on a digitalsignal processor, ASIC, microprocessor, or other type of processoroperating on a computer system, such as a personal computer, server, orother computer system, turning such computer system into a specificallyprogrammed machine.

Examples, as described herein, may include, or may operate on,processors, logic, or a number of components, modules, or mechanisms(herein “modules”). Modules are tangible entities (e.g., hardware)capable of performing specified operations and may be configured orarranged in a certain manner. In an example, circuits may be arranged(e.g., internally or with respect to external entities such as othercircuits) in a specified manner as a module. In an example, the whole orpart of one or more computer systems (e.g., a standalone, client orserver computer system) or one or more hardware processors may beconfigured by firmware or software (e.g., instructions, an applicationportion, or an application) as a module that operates to performspecified operations. In an example, the software may reside on amachine readable medium. The software, when executed by the underlyinghardware of the module, causes the hardware to perform the specifiedoperations.

Accordingly, the term “module” is understood to encompass a tangiblehardware and/or software entity, be that an entity that is physicallyconstructed, specifically configured (e.g., hardwired), or temporarily(e.g., transitorily) configured (e.g., programmed) to operate in aspecified manner or to perform part or all of any operation describedherein. Considering examples in which modules are temporarilyconfigured, each of the modules need not be instantiated at any onemoment in time. For example, where the modules comprise ageneral-purpose hardware processor configured using software, thegeneral-purpose hardware processor may be configured as respectivedifferent modules at different times. Software may accordingly configurea hardware processor, for example, to constitute a particular module atone instance of time and to constitute a different module at a differentinstance of time.

Those skilled in the art will appreciate that while the disclosurecontained herein pertains to the provision of electrical power tovehicles, it should be understood that this is only one of many possibleapplications, and other embodiments including non-vehicular applicationsare possible. For example, those skilled in the art will appreciate thatthere are numerous non-vehicle inductive charging applications such asportable consumer electronic device chargers, such as those (e.g.,PowerMat™) used to charge toothbrushes, cellular telephones, and otherdevices. Accordingly, these and other such applications are includedwithin the scope of the following claims.

What is claimed is:
 1. A coil array comprising an n×m array of coilassemblies, where n≥1 and m≥2, arranged in a rectilinear x-y gridpattern, each coil assembly generating a charging signal at a frequencythat is out-of-phase with a charging signal of a neighboring coilassembly during a charging session whereby a charging signal transmittedby a coil assembly destructively interferes with a charging signaltransmitted by the neighboring coil assembly to reduce additive magneticflux density during charging as compared to additive magnetic fluxdensity where the neighboring coil assembly is in-phase during charging.2. The coil array of claim 1, wherein the coil array is mounted in theground and further comprises a communication device associated with thecoil array that receives setup parameters from a communication deviceassociated with a vehicle to be charged and a charging site server thatsets charging parameters of the coil array using the setup parameterswhereby the additive magnetic flux density during charging remainspredominately within an exclusion zone for the vehicle.
 3. The coilarray of claim 1, wherein each coil assembly is driven by a differentpower source and each coil assembly transmits a charging signal having adetermined amplitude.
 4. The coil array of claim 1, wherein the chargingsignal transmitted by the coil assembly is approximately 180° out ofphase with the charging signal transmitted by the neighboring coilassembly.
 5. The coil array of claim 1, wherein n=2 and m=2, the coilarray comprising a first pair of coil assemblies disposed adjacent eachother and a second pair of coil assemblies disposed adjacent each otherand in parallel with the first pair of coil assemblies, said first andsecond pairs of coil assemblies being powered by respective first andsecond power sources or each coil assembly being powered by a separatepower source, wherein each of the first and second pairs of coilassemblies shares a same transmission frequency and power level but witha set phase difference between the coil assemblies in each pair of coilassemblies.
 6. The coil array of claim 1, wherein n=2 and m=2, the coilarray comprising a first pair of coil assemblies disposed diagonallyfrom each other and a second pair of coil assemblies disposed diagonallyfrom each other and side-by-side in the x-y directions with the firstpair of coil assemblies, said first and second pairs of coil assembliesbeing powered by respective first and second power sources or each coilassembly being powered by a separate power source, wherein the firstpair of coil assemblies shares a first frequency and power level and thesecond pair of coil assemblies shares a second frequency and powerlevel, the first and second frequencies being different, whereby eachcoil assembly has a set phase difference with adjacent coil assembliesin the x-y directions during charging.
 7. The coil array of claim 1,wherein n=2 and m=2, the coil array comprising a first pair of coilassemblies disposed side-by-side with each other and a second pair ofcoil assemblies disposed side-by-side with each other and in parallelwith the first pair of coil assemblies, said first and second pairs ofcoil assemblies being powered by respective first and second powersources or each coil assembly being powered by a separate power source,wherein the first pair of coil assemblies shares a first frequency andpower level and the second pair of coil assemblies shares a secondfrequency and power level, the first and second frequencies beingdifferent, whereby each coil assembly has a set phase difference withadjacent coil assemblies in the x-y directions during charging.
 8. Thecoil array of claim 1, wherein n=1 and m=3, the coil array comprisingrespective first, second and third coil assemblies in a row, wherein thefirst and third coil assemblies output first charging signals having afirst frequency, phase, and power level and the second coil assembly isdisposed between the first and third coil assemblies and outputs asecond charging signal having the first frequency and power level butthe second charging signal is out-of-phase with the first chargingsignal.
 9. The coil array of claim 1, wherein n=1 and m=3, the coilarray comprising respective first, second and third coil assemblies in arow, wherein the first and third coil assemblies output first chargingsignals having a first frequency, first phase, and first power level andthe second coil assembly is disposed between the first and third coilassemblies and outputs a second charging signal having the firstfrequency but the second charging signal is out-of-phase with the firstcharging signal and has a second power level that is different from thefirst power level that is set so as to reduce the additive magnetic fluxdensity as compared to an additive magnetic flux density where thefirst, second, and third coil assemblies output charging signals havinga same power level.
 10. The coil array of claim 9, wherein the first andsecond power levels are adjusted to shape the additive magnetic fluxdensity during charging to remain predominately within the exclusionzone for the vehicle.
 11. The coil array of claim 9, wherein the firstand second power levels are set to a region where a maximum magneticflux cancellation between the first and second charging signals occurson a curve that is a function of a current ratio between the first andthird coil assemblies versus the second coil assembly and a proportionof magnetic flux density canceled when the first and third coilassemblies carry current that is approximately 180° out of phase with acurrent carried by the second coil assembly, the first and second powerlevels being set approximate a point where a minimum magnetic fluxcancellation between the first and second charging signals has agreatest proportion of magnetic flux density.
 12. The coil array ofclaim 1, wherein n=2 and m=3, the coil array comprising a first pair ofcoil assemblies disposed adjacent each other, a second pair of coilassemblies disposed adjacent each other, and a third pair of coilassemblies disposed adjacent each other, each pair of coil assembliesbeing in parallel with each other and outputting first charging signalshaving a first frequency, each pair of coil assemblies being powered byrespective first and second power sources or each coil assembly in eachpair being powered by a separate power source, wherein a coil assemblyof each pair of coil assemblies outputs a charging signal having a setphase difference with an adjacent coil assembly in the x-y directionsduring charging.
 13. The coil array of claim 1, wherein n=2 and m=3, thecoil array comprising a first pair of coil assemblies disposed adjacenteach other, a second pair of coil assemblies disposed adjacent eachother, and a third pair of coil assemblies disposed adjacent each other,each pair of coil assemblies being in parallel with each other andoutputting first charging signals having a first frequency, each pair ofcoil assemblies being powered by respective first and second powersources or each coil assembly in each pair being powered by a separatepower source, wherein a first coil assembly in each pair of coilassemblies has a set phase difference with a second coil assembly ofeach pair of coil assemblies, and wherein a coil assembly of each pairof coil assemblies outputs a charging signal having a same phase as acharging signal output by an adjacent coil assembly of an adjacent pairof coil assemblies.
 14. The coil array of claim 1, wherein each coilassembly generates a charging signal at the frequency where the chargingsignal is between 25° and 180° out-of-phase with a charging signal of anadjacent coil assembly during a charging session.
 15. A wireless powertransfer system comprising: a vehicle coil array comprising an n×m arrayof vehicle coil assemblies, where n≥1 and m≥2, arranged in a rectilinearx-y grid pattern, each vehicle coil assembly receiving a charging signalat a frequency that is out-of-phase with a charging signal of anadjacent vehicle coil assembly during a charging session whereby acharging signal received by each vehicle coil assembly destructivelyinterferes with a charging signal received by an adjacent vehicle coilassembly in the x-y directions so as to reduce additive magnetic fluxdensity during charging as compared to additive magnetic flux densitywhere the adjacent vehicle coil assemblies in the x-y directions arein-phase during charging; and a ground coil array comprising an r×sarray of coil assemblies, where r≥n and s≥m, arranged in a rectilinearx-y grid pattern, each ground coil assembly generating the chargingsignal at the frequency whereby the charging signal is out-of-phase withthe charging signal of an adjacent ground coil assembly during acharging session and whereby the charging signal generated by eachground coil assembly destructively interferes with the charging signalgenerated by an adjacent ground coil assembly in the x-y directions soas to reduce additive magnetic flux density during charging as comparedto additive magnetic flux density where the adjacent ground coilassemblies in the x-y directions are in-phase during charging.
 16. Thewireless power transfer system of claim 15, wherein the ground coilarray detects when a vehicle coil assembly is inoperative and activatesonly the ground coil assemblies aligning with operative vehicle coilassemblies to send charging signals.
 17. The wireless power transfersystem of claim 15, further comprising a data repository that isaccessible by at least one of the vehicle coil array or the ground coilarray during a charging session to access a charging profile of defaultand historical measurements for each vehicle coil assembly, the chargingprofile including frequency response and charging models for settingcharging parameters during the charging session.
 18. The wireless powertransfer system of claim 17, wherein the charging profile comprises atleast one of vehicle coil assembly frequency offset; make, model, andmanufacturer of the ground coil assembly; a number of vehicle coilassemblies; positioning of the vehicle coil assemblies; minimum andmaximum current and voltage support of the vehicle coil assembly; healthstatus of the vehicle coil assemblies; temperature limitations of thevehicle coil assemblies; temperature readings of vehicle coilassemblies; or cooling availability for the vehicle coil assemblies. 19.The wireless power transfer system of claim 17, wherein the ground coilarray obtains a number and placement of vehicle coil assemblies of avehicle to be charged from the charging profile for the vehicle to becharged and selects, for sending charging signals, a pattern of groundcoil assemblies from the r×s array of coil assemblies corresponding tothe number and placement of the vehicle coil assemblies for the vehicleto be charged.
 20. The wireless power transfer system of claim 17,wherein the data repository further stores charging parameters for theground coil assembly including magnetic signal characteristics for eachground coil assembly or pair of ground coil assemblies based on analigned vehicle coil assembly or pair of vehicle coil assemblies. 21.The wireless power transfer system of claim 20, wherein the chargingparameters for the ground coil assembly include at least one ofinstantaneous power level during a charging session, charging signalfrequency, frequency drift, signal phase offset, or nominal coil-to-coilgap.
 22. The wireless power transfer system of claim 20, wherein thecharging parameters for the ground coil assembly include at least one ofpower availability; environmental factors; or ground coil assemblyconditions including at least one of internal temperature, usage, numberof coils per ground coil assembly, number of turns per ground coilassembly, or whether the ground coil assembly is surface mounted orflush mounted.
 23. The wireless power transfer system of claim 20,wherein the charging parameters for the ground coil assembly include atleast one of make, model, and manufacturer of the ground coil assembly;autonomous alignment capability of the ground coil assembly; minimum andmaximum current and voltage support of the ground coil assembly;communications protocols available to the ground coil assembly; or acommunications bandwidth of the ground coil assembly.
 24. A wirelesspower transfer system comprising: a vehicle coil array comprising an n×marray of vehicle coil assemblies, where n≥1 and m≥2, arranged in arectilinear x-y grid pattern, each vehicle coil assembly generating acharging signal at a frequency whereby the charging signal isout-of-phase with a charging signal of an adjacent vehicle coil assemblyduring a charging session and whereby a charging signal generated byeach vehicle coil assembly destructively interferes with the chargingsignal generated by an adjacent vehicle coil assembly in the x-ydirections so as to reduce additive magnetic flux density duringcharging as compared to additive magnetic flux density where theadjacent vehicle coil assemblies in the x-y directions are in-phaseduring charging; and a ground coil array comprising an r×s array ofground coil assemblies, where r≥n and s≥m, arranged in a congruentrectilinear x-y grid pattern, each ground coil assembly receiving thecharging signal at the frequency whereby the charging signal isout-of-phase with the charging signal of an adjacent ground coilassembly during a charging session and whereby the charging signalreceived by each ground coil assembly destructively interferes with thecharging signal received by an adjacent ground coil assembly in the x-ydirections so as to reduce additive magnetic flux density duringcharging as compared to additive magnetic flux density where theadjacent ground coil assemblies in the x-y directions are in-phaseduring charging.
 25. A wireless power transfer system comprising: aground coil array comprising an n×m array of ground coil assemblies,where n≥1 and m≥2, arranged in a rectilinear x-y grid pattern, eachground coil assembly generating a charging signal at a frequency wherebythe charging signal is out-of-phase with a charging signal of anadjacent ground coil assembly during a charging session and whereby acharging signal generated by each ground coil assembly destructivelyinterferes with the charging signal generated by an adjacent ground coilassembly in the x-y directions so as to reduce additive magnetic fluxdensity during charging as compared to additive magnetic flux densitywhere the adjacent ground coil assemblies in the x-y directions arein-phase during charging; and a vehicle coil array comprising an r×sarray of vehicle coil assemblies, where r≥n and s≥m, arranged in arectilinear x-y grid pattern, each vehicle coil assembly receiving thecharging signal at the frequency whereby the charging signal isout-of-phase with the charging signal of an adjacent vehicle coilassembly during a charging session and whereby the charging signalreceived by each vehicle coil assembly destructively interferes with thecharging signal received by an adjacent vehicle coil assembly in the x-ydirections so as to reduce additive magnetic flux density duringcharging as compared to additive magnetic flux density where theadjacent vehicle coil assemblies in the x-y directions are in-phaseduring charging.
 26. An electric vehicle charging system comprising: aplurality of coil arrays, each coil array comprising at least one coilassembly that generates a charging signal at a set frequency; at leastone sensor that measures aggregate magnetic flux generated by chargingsignals generated by the coil arrays; and means for identifying anadditive hot spot of magnetic flux densities and for adjusting at leastone of power, phase, and frequency offsets of at least one of the coilarrays in a vicinity of the additive hot spot of magnetic flux densitiesto reduce magnetic flux densities at the additive hot spot of magneticflux densities.
 27. A method of charging an electric vehicle,comprising: a charging point and the electric vehicle initiatingcommunications with each other; the charging point receiving setup datafrom the electric vehicle for setting up the charging point for chargingof the electric vehicle, the setup data including at least one of amanufacturer of the electric vehicle, a model of the electric vehicle,or an exclusion zone; and the charging point activating ground primarycoils and associated power levels for the activated ground primary coilsbased on the setup data to create a charging signal having a magneticflux density that predominately remains within the exclusion zone. 28.The method of claim 27, further comprising using at least one of themanufacturer or model of the electric vehicle to look up in a databasewhich ground primary coils to activate and power levels for theactivated ground primary coils.
 29. The method of claim 27, wherein thecharging point activates the ground primary coils according to adetermined layout of the secondary coils of the electric vehicle asdetermined from the received setup data.
 30. The method of claim 27,wherein the charging point adjusts parameters of the charging signalbased on the setup data as needed to fit a magnetic flux generated bythe charging signal predominately within the exclusion zone.
 31. Themethod of claim 27, wherein the charging point and the electric vehicleinitiating communications with each other comprises the charging pointemitting an inductive communications beacon while in a standby state andreceiving a response from the electric vehicle to establish that theelectric vehicle is approaching the charging point.